Leucippus

Leucippus (fl. 5th century BC) was a Presocratic Greek philosopher who worked with his student Democritus to develop the theory of "atomism".

Biography
Leucippus was born in Miletus, Ionia, and he belonged to the same Ionian school of philosophy as Thales of Miletus, Anaximander, and Anaximenes. He was the master to his pupil Democritus, a philosopher from Thrace, and the two of them worked together to coin the theory of "atomism", arguing that everything was composed entirely of various imperishable, indivisible elements called atoms.